With my brand new profile (with very minimal changes apart from adding my 3 imap accounts and the local folders), same result: after working fine for a while, Thunderbird freezes right after sending an email and does not come back (waited more than 5 minutes before killing the process). Sometimes I can send numerous emails and work for a couple of hours without any problem (was like that yesterday), but this morning, it took less than 20 minutes for TB to freeze.

I guess the next step is to adjust this new profile by going again through the list of potential issues? (mac spotlight, gmail all mail folder, global search, place a copy in, gmail smtp settings, auto save, and check for new emails)

With the new profile: - Global Search and Indexer: changed to disable - Gmail accounts, 'Place a copy in': changed to disable - Changed gmail smtp: port 587, STARTTLS, OAuth2, User name = email address. (this is not the default setting when setting up a new profile, mine was initially 465 and SSL/TLS) - Changed checks for new mail from every 10 minutes to every 15 minutes. - Disabled checks for new messages. - Disabled "Auto Save every" (Preferences, Composition, General, Auto Save every) - Disabled "Allow immediate server notifications when new messages arrive" - Allow Spotlight to search messages: was disabled by default - Gmail All Mail folder: was unsubscribed by default - Is panacea.dat cache file in your profile too big? Mine is only 367kB - Address Book: with the new profile, I only have 1836 contacts

With the new profile and all of the above, I'm still getting the same issue: Thunderbird sometimes freezes (and remains frozen until I kill the process) right after sending an email. I'm left with no other things to try to sort out the issue.

I would've recommended a new profile with just one account, with minimal or no existing mail, to start with the simplest possible setup, with all the usual restrictions, e.g. no antivirus scanning, no windows search etc. By adding 3 accounts and the old Local Folders, you may be making it difficult to isolate the source of the problem.

Great tip. And with the profile approach, I noticed I can have multiple Thunderbird instances running simultaneously so it's not really a problem to have just a single account in the profile I'm trying to debug. Everything is set up and I'm waiting to see what will happen.

With the new profile (only one gmail account): - Allow Spotlight to search messages: was disabled by default - Global Search and Indexer: changed to disable - Disabled "Auto Save every" (Preferences, Composition, General, Auto Save every) - Changed gmail smtp: port 587, STARTTLS, OAuth2, User name = email address. (this is not the default setting when setting up a new profile, mine was initially 465 and SSL/TLS) - Gmail accounts, 'Place a copy in': changed to disable - Disabled checks for new messages. - Disabled "Allow immediate server notifications when new messages arrive" - Gmail All Mail folder: was unsubscribed by default

With the new profile and all of the above, I still get the same behavior: every now and then, after sending an email, Thunderbird freezes. I even waited more than 30 minutes and it remained "not responding" and I had to kill the process.

The only "unusual" thing I can see about my profile is that the gmail account is a "corporate" gmail, meaning that it is not an @gmail.com address.

I'll continue to use the new profile to see how "regularly" Thunderbird freezes. If you have new ideas to try to debug the problem, let me know.

Are you by any chance connecting to the internet through a VPN, and is Time Machine (Mac) disabled?

I'm not using a VPN; I'm only behind a typical corporate firewall.

Time Machine is enabled. Reading between the lines, I suspect that my next move would be to disable it to see if it helps? Or should I instruct Time Machine from neglecting the profiles folder (or some other folder)?

Time Machine is noted in section 3.) of the performance article. I would first disable it entirely, and if it makes a difference, then try excluding the TB profile folder.

Try also running the computer in Windows or OS X safe mode to test if some other external program is causing the problem. With a corporate network, I would also consider the possibility there's a network-wide security program acting on email, that may be beyond your control. If the same TB profile performs differently on, e.g., your home network, that would support that idea.

Even with Time Machine disabled, I'm experiencing the same issue: TB freezes every now and then when sending an email, and this happens multiple times a day. I'm sending 10-30 emails a day, so it freezes maybe every 5-10 emails.

I previously tried running TB in safe mode and TB had the same behavior (freezing after sending an email). Running in safe mode renders my Mac almost unusable (it is very slow), so I did not try safe mode together with the new TB profile using a single account. Nevertheless, I would be very surprised if it made any difference.

I cannot bring Mac outside of the corporate network (it's a desktop/large iMac).

If you can't take the Mac outside of the network, I thought you could make a copy of the profile or Thunderbird folder, with all user data, and run it on a Mac on another network.

After trying pretty much everything, my next bet would be to debug the beast myself. Is this the best place to start? https://developer.mozilla.org/en-US/docs/Mozilla/Developer_guide/Build_Instructions/Simple_Thunderbird_build

I'm not really qualified to recommend this for solving your problem, but you're welcome to try. If the issues is strictly with TB and not due to 3rd-party programs or hardware flaws, I'd be more inclined to start with a very simple setup in a new profile and gradually add more structure until problems arise.